The atmospheric pressure detected by the atmospheric pressure sensor is normally applied to the calculation of control parameters for the internal combustion engine, such as the fuel supply amount and the ignition timing. It is preferable to reduce the number of the sensors for calculating the engine control parameters as much as possible.
Patent document 1 (shown below) discloses a method for estimating an atmospheric pressure according to an intake pressure, an intake air temperature, an intake air flow rate, a throttle valve opening, and an idling control valve opening.
According to this atmospheric pressure estimating method, a flow related term FT is calculated using the intake pressure, the intake air temperature, and the intake air flow rate which are detected. The effective area term Aint is calculated from the throttle valve opening and the idling control valve opening. Subsequently, the pressure ratio map preliminarily set is retrieved according to the flow related term FT and the effective area term Aint, to calculate a pressure ratio (PA/MAP) of the atmospheric pressure PA with respect to the intake pressure MAP. The estimated atmospheric pressure is calculated by multiplying the intake pressure MAP by the pressure ratio (PA/MAP).